1. Field of the Invention
The present invention relates to a coating composition used for rough texture-surface finish, capable of forming a coating film which is superior in processability, corrosion resistance, adhesivity, impact resistance, scratch resistance, etc. and which has a rough texture, particularly a coating composition suitable for imparting rough texture-surface finish in one layer-coating; a process for producing a one layer-coated steel plate, which comprises coating the above coating composition; and a one layer-coated steel plate which is a steel plate having thereon a cured film of the above coating composition and which is suitable for processing into various articles.
2. Description of the Prior Art
As coated steel plates to be processed into various household electric or electronic appliances wherein decorativeness is required, such as VTR, radio with cassette tape recorder and CD player, electronic oven, washing machine, refrigerator and the like, there were proposed coated steel plates obtained by coating, on a steel plate, a coating for rough texture-surface finish (which is a dispersion of organic polymer fine particles in a binder) as an outermost layer [such coated steel plates are described in, for example, Japanese Patent Application Kokai (Laid-Open) No. 168967/1982 (corresponding to U.S. Pat. No. 4,457,965 and GB-A-094,815) and Japanese Patent Application Kokai (Laid-Open) No. 74970/1987].
Of these coated steel plates, two layer-coated steel plates are in practical application, and they are obtained by coating, on a galvanized steel plate subjected to a chemical treatment, a coating for rough texture-surface finish (which is a dispersion of organic polymer fine particles in a binder) as an outermost layer via an undercoat of polyester or epoxy type to form a cured film of the coating on the steel plate. In production of two layer-coated steel plate, since the coating steps are many, there are required rationalization of coating, coating in shorter time, coating in thinner film or/and one layer-coating (the latter two items lead to resource saving). Application of a conventional coating for rough texture-surface finish, directly on a galvanized steel plate gives a coating film inferior in processability, corrosion resistance, adhesivity, scratch resistance, etc.
Hence, the present inventors made a study with an aim of developing a one layer-coated steel plate capable of forming a coating film superior in processability, corrosion resistance, adhesivity, impact resistance, scratch resistance, etc. As a result, the present inventors found out that the above aim can be achieved by coating, on a zinc or zinc alloy plated steel plate subjected to a chromate chemical treatment, directly and not via an undercoat, a coating comprising a particular hydroxyl group-containing polyester resin, a particular melamine resin, a rust preventive pigment and organic polymer fine particles. The present invention has been completed based on the finding.